This Core provides instrumental support and technical expertise for quantitative and qualitative analyses. This includes, e.g., automated quantitation of nitrate and nitrate/nitrite; measurement of '5N in nitric oxide, nitrate, or nitrosamines; quantitation of alkylated purines; methyl-, dimethyl-, and trimethylamine; thymine, xanthine, guanine, 8-oxoguanine, and 5-hydroxymethyluracil, etc.; quantitation and characterization of volatile N-nitroso compounds; free nitric oxide and nitrous oxide; glutathione (GSH), GSSG, and S-nitrosoglutathione; molecular weight determination for modified or unmodified proteins, peptides, or oligonucleotides; characterization of synthetic model compounds and experimental reaction products; characterization of modified and unmodified peptides and oligonucleotides. Major equipment includes three mass spectrometers, i.e., a Hewlett Packard 5989A GC-MS (with electron ionization, positive chemical ionization, and negative ion chemical ionization), a Hewlett Packard 5989B electrospray. mass spectrometer, and a Finnigan TSQ7000 tandem mass spectrometer with electrospray, atmospheric pressure chemical ionization, and nanoelectrospray. The HP 5989B has open-access for routine electrospray MS. Other equipment includes liquid chromatographs (detection by diode- array, fluorescence, electrochemistry, and laser-induced fluorescence (LIF)), uv-visible spectrophotometers, a nitric oxide delivery system. The specific objectives for the Core derive from those of the Program Projects, and may include development of analytical methods for systems such as the reaction of 8-oxo-2'-deoxyguanosine with peroxynitrite or development of software to interpret the collisionally-induced decomposition mass spectra of modified oligonucleotides. In addition to objectives that arise during a project, the Core has objectives to enhance its overall capabilities, e.g., assessment of capillary LC with LIF detection as an ultrasensitive method for quantitating nitric oxide-related and peroxynitrite-related DNA and protein damage, and nanoelectrospray and microelectrospray for the characterization of unknowns.